CN1122062C - Process for producing PET articles with low acetaldehyde - Google Patents

Abstract

The present invention discloses a process for producing molded, shaped or extruded articles comprising the steps of: a) melt reacting, in the presence of a catalyst which is substantially free of Co compounds, at least one glycol and at least one dicarboxylic acid to form a polyester having an I.V. of at least about 0.5 dL/g, wherein said at least one glycol is selected from the group consisting of glycols having up to 10 carbon atoms and mixtures thereof and said dicarboxylic is selected from the group consisting of alkyl dicarboxylic acids having 2 to 16 carbon atoms, aryl dicarboxylic acids having 8 to 16 carbon atoms and mixtures thereof; b) adding an acetaldehyde reducing additive to said polyester to form a reduced acetaldehyde polyester; and c) forming said reduced acetaldehyde polyester into articles directly from step b. Thus, the present invention provides a process for directly producing from the melt article having extremely low acetaldehyde content.

Description

Manufacturing method of PET products with low acetaldehyde content

This application is based upon and claims priority from Provisional Application 60/028,625, filed October 28,1996.

Background of the invention

Polyesters are widely used to make fibers, molded articles, films, sheets, food trays, and food and beverage containers. Such polymers are generally produced by batch or continuous melt phase polycondensation well known in the art. The polymer is then pelletized by various extrusion or molding operations. In certain applications where higher molecular weight polymers are desired, the pellets are subjected to "solid state" polycondensation conditions where the inherent viscosity (I.V.) value increases significantly. This solid state polycondensation reaction is used for two reasons. First, because the melt viscosity of polyester polymers is high for polymers with I.V. values greater than about 0.6, solid state conditioning provides a convenient means of post-processing the polymer. Second, the method of solid-state conditioning provides conditions for removal of unwanted volatile impurities such as acetaldehyde, which is important in certain applications. Also, small amounts of moisture are known to degrade polyesters when they are melt processed in conventional equipment. Therefore, the polyester is generally carefully dried in a drier to a very low moisture content prior to melt processing. The drying process also removes some unwanted volatiles other than water.

During the manufacture or processing of polyesters such as polyethylene terephthalate (PET), certain by-products are formed in the melt phase. One such by-product is acetaldehyde, the presence of which in molded articles such as food containers, beverage bottles, water bottles, etc. is detrimental from a taste standpoint. Especially for sensitive beverages such as cola, beer and water, it is highly desirable to produce container preforms for use in blow molding processes with acetaldehyde levels of less than about 10 ppm. However, achieving such low levels of acetaldehyde is difficult because, as is well known to practitioners of the prior art, acetaldehyde is a by-product during the polymerization and subsequent melt processing of PET and similar polymers. Forming.

Thus, prior to the discovery of the present invention, a four-step process was commonly practiced to obtain polyesters suitable for those applications where it was important to minimize the acetaldehyde content. Such methods generally involve the preparation of lower molecular weight prepolymers having I.V. values of about 0.3-0.6 by melt phase polymerization techniques known in the art. Depending on the reaction conditions chosen, the acetaldehyde content of such prepolymers can range from about 30 to over 150 ppm. This prepolymer is then cooled, shaped into pellets, crystallized and subjected to further solid state polymerization at lower temperatures. Generally speaking, the diol, acetaldehyde and other reaction by-products are extracted from the pellets with gas so that at the end of the solid phase process, the I.V. value increases to about 0.75 or greater and the acetaldehyde content is reduced to about 1 ppm or lower.

After solid state conditioning, polyesters are generally shipped and stored in ambient air (from which they absorb moisture). Thus, as a third step, the polymer is generally dried immediately before being reheated, melted and formed into useful shapes such as beverage bottle stock. Processing generally causes a small decrease in the I.V. of the polymer, and the acetaldehyde content increases from less than 1 ppm in pellets to about 8 or 10 ppm or more in shaped articles. Although the melt processing is generally complete within a minute or two, the acetaldehyde level miraculously increases.

US Patent Nos. 5,266,413, 5,258,233 and 4,8837,115 disclose various polyamides for reducing acetaldehyde content in PET. US Patent Application Serial No. 595,460, filed February 5, 1996, discloses novel polyesteramide compositions for reducing the acetaldehyde content of PET.

Japanese patent application Zhao 62-182065 (1987) discloses blending nylon 6 and other aliphatic polyamides in PET. When the residence time in the molten state is within 60 seconds, the acetaldehyde content will be reduced to below 10ppm .

Several other compounds are also disclosed as useful for reducing acetaldehyde levels. These include ethylenediaminetetraacetic acid (US Patent 4,357,461), alkoxylated polyols (US Patent 5,250,333), bis(4-beta-hydroxyethoxyphenyl)sulfone (US Patent 4,330,661), zeolite compounds (US Patent Patent 5,104,965), 5-hydroxyisophthalic acid (US Patent 4,093,593), polyethylene isophthalate (US Patent 4,403,090), supercritical carbon dioxide (US Patents 5,049,647 and 4,764,323), and protic acid catalysts (US Patent 4,447,595 and 4,424,337).

US Patent No. 4,361,681 discloses that capping the hydroxyl groups of PET with an anhydride such as succinic anhydride or phthalic anhydride will suppress the formation of acetaldehyde. US Patent 5,243,020 discloses pyromellitic anhydride capping PET.

US Patent 4,356,299 discloses that the use of catalysts based on low levels of Ti and Sb is beneficial in limiting the amount of acetaldehyde formed.

US Patent 5,656,719 discloses a process for making molded polyesters with low acetaldehyde content by melt polymerization and finishing reactors. The finishing reactor operates at low vacuum levels and long residence times to increase the I.V.

US Patent 5,656,221 discloses the manufacture of polyester molded articles with low acetaldehyde content by adding acetaldehyde reducing additives and direct molding from melt polymerization. In addition to the usual polymerization catalyst, cobalt compound needs to be added in an amount of 5-120ppm.

Also disclosed are some PET articles with low acetaldehyde content but no integrated method of adding acetaldehyde reducing agent. US Patent Application Serial No. 609,197 describes the direct molding of polyester from the melt. US Patent Application Serial No. 498,404 discloses methods and apparatus for distributing molten PET to multiple molding machines. US Patent No. 5,648,032 describes a process for making low acetaldehyde content polyethylene terephthalate without the use of solid state adjusted polymers.

Several patents disclose devolatilization of polymers using vented extruders. US Patent 5,597,891 discloses the use of purge gas in a vented extruder to make reduced acetaldehyde content polyester articles. US Patent 5,102,594 discloses a method of supplying a powdered thermoplastic polycondensation polymer to a vented extruder. US Patent 3,486,864 discloses the use of vacuum to remove volatile diols from remelted prepolymers as quickly as possible. US Patent 3,913,796 discloses a method of heating solid resin into a semi-molten state using an extrusion screw, while US Patent 4,060,226 discloses a method of removing oxygen by means of a one-way valve.

Brief description of the drawings

Figure 1 is a flow chart showing several possible embodiments of the process of the present invention.

Summary of the invention

The present invention encompasses a method by which low acetaldehyde content polyesters such as PET or similar polymers can be prepared without solid state conditioning and conventional drying of solid pellets. Surprisingly, the present invention can be carried out without a catalyst of Co compounds or a finishing reactor.

The invention specifically includes a method of manufacturing a molded article comprising the steps of:

a) subjecting at least one diol and at least one dicarboxylic acid to a melt reaction in the presence of a catalyst substantially free of Co compounds to form a polyester having an I.V. value of at least about 0.5 dL/g, wherein the at least one diol is selected from Diols having not more than 10 carbon atoms and mixtures thereof, and the dicarboxylic acids are selected from alkyl dicarboxylic acids having 2 to 16 carbon atoms, aryl dicarboxylic acids having 8 to 16 carbon atoms and their mixtures;

b) adding an acetaldehyde reducing agent to said polyester, and subsequently devolatilizing said polyester to form a low acetaldehyde content polyester; and

c) Shaping said reduced acetaldehyde content polyester directly from step b) into shaped articles. In addition, several optional steps such as melt devolatilization, granulation, storage, transportation, remelting and drying may be included to suit the requirements of a particular process. If the polymer is pelletized, the acetaldehyde reducing agent can be added before pelletizing or after remelting. Shaped articles produced by the method of the invention exhibit surprisingly low acetaldehyde contents.

Invention Narrative

As used herein, the term "I.V." refers to the inherent viscosity of a solution of 0.5 g of polymer dissolved in 100 mL of a mixture of phenol (60% by volume) and tetrachloroethane (40% by volume).

The present invention provides a process that enables the manufacture of shaped articles from polymers exhibiting both high molecular weight and low acetaldehyde content without the use of solid state polymerization, solid state devolatilization, or finishing reactors.

Specifically, a preferred embodiment of the present invention provides an improved "melt to mold" process in which a polyester polymer or copolymer is molded in the melt phase Prepared to achieve an I.V. value of greater than about 0.5 dL/g; adding an acetaldehyde reducing additive to the polymer melt and then feeding the melt directly from the polycondensation reactor to at least one molding or forming machine. No intervening finishing or I.V. growth steps are required.

For the polycondensation, any conventional melt polymerization process capable of producing the desired I.V. may be used, and the reactor may comprise one or several reaction tanks or reaction zones capable of producing a polyester having the desired I.V.

The I.V. is preferably at least 0.65 dL/g so that the polymer obtained directly from the melt has sufficient molecular weight to provide high performance molded articles such as containers. In the present invention, the desired I.V. is produced in the polycondensation reaction without the need for a finishing reactor.

In general, this melt polymerization is carried out under conditions known in the art, however for the present invention no addition of Co compounds is necessary.

The acetaldehyde reducing agent can be any known acetaldehyde reducing additive. Suitable additives include polyamides disclosed in U.S. Patents 5,266,413, 5,258,233, and 4,8837,115, polyesteramides such as those disclosed in U.S. Patent Application Serial No. 595,460 filed on February 5, 1996, polyesteramides such as those disclosed in Japanese Patent No. - Nylon 6 and other aliphatic polyamides disclosed in 62-182065 (1987), ethylenediaminetetraacetic acid (US Patent 4,357,461), alkoxylated polyols (US Patent 5,250,333), bis(4-beta-hydroxy Ethoxyphenyl) sulfone (US patent 4,330,661), zeolite compound (US patent 5,104,965), 5-hydroxyisophthalic acid (US patent 4,093,593), polyethylene isophthalate (4,403,090), supercritical carbon dioxide (US Patents 5,049,647 and 4,764,323) and protic acid catalysts (US Patents 4,447,595 and 4,424,337). Preferred acetaldehyde reducing agents are selected from polyamides, polyesteramides and polyethylene isophthalate. Suitable polyamides include homo- and co-polyamides with AB structure or _A2B2 structure, such as polycaprolactam, polyhexamethylene adipamide, polym-xylylene adipamide _, and the like. Branched or highly branched polyamides can also be used.

Suitable polyester amides include those prepared from terephthalic acid, 1,4 cyclohexanedimethanol, isophthalic acid and hexamethylenediamine (diacid to diamine ratio is preferably 50:50, diol to The diamine ratio is preferably 50:50), polyester amides prepared from terephthalic acid, 1,4-cyclohexanedimethanol, adipic acid and hexamethylenediamine, terephthalic acid, 1,4-cyclohexanedimethanol Polyesteramide prepared from hexanedimethanol and bis(p-aminocyclohexyl)methane. Other known scavengers, such as polyethyleneimine, can also be used.

The addition amount of the acetaldehyde reducing agent is generally about 0.1-5% (weight). More preferably, about 0.2-3% by weight of the additive is added. It should be understood that the additives may be added individually or as concentrates in compatible polymer-based resins.

The polymer devolatilization process can also be used simultaneously with the acetaldehyde reducing agent to further remove the generated acetaldehyde and other unwanted volatiles. It can be in a separate devolatilization unit and at the same time in the polycondensation reactor Or a simultaneous devolatilization step in the molding machine.

The devolatilizer may be any device known in the art for producing a large surface area per unit volume and/or for rapid regeneration of exposed melt surfaces. As described in US Pat. No. 5,597,891, the devolatilization unit subjects the liquid surface to a low partial pressure of acetaldehyde by purging an inert gas, or applying a vacuum, or both. The devolatilizer can be a vented single screw extruder (US Patent 4,107,787), a vented twin screw extruder (US Patent 3,619,145), a rotary disc processor (US Patent 4,362,852) or a polymer production line material (US Patent 3,044,993). All of these are incorporated herein by reference. The present invention carries out the devolatilization step at a pressure above about 25 mmHg, preferably at a pressure below or near atmospheric pressure. The residence time should be short enough not to cause a significant increase in I.V. For the purposes of the present invention, a substantial increase in I.V. is an increment greater than about 0.1 dL/g, preferably greater than about 0.05 dL/g, more preferably greater than about 0.03 dL/g.

Several additional optional steps may also be added to the method of the present invention. These steps include: melt devolatilization, granulation, storage, transportation, remelting and drying. It should be understood that these optional steps may be used alone (ie, devolatilization), or in combination with each other (granulation and remelting, or storage, transport and remelting, etc.). Suitable combinations of optional steps are known in the art and need not be detailed here.

Figure 1 illustrates the many possible combinations of operations, from high molecular weight melt phase polymers to molded articles. A preferred combination of operations is represented on Figure 1 as path G, i.e. preparing the polymer in the molten state to the desired I.V., adding additives and processing the improved polymer melt into useful shaped articles, such as blanks for beverage bottles, so The described articles have unexpectedly low acetaldehyde content.

A second combination of operations is depicted in Figure 1, Route N, which is to prepare the polymer in the melt to the desired I.V., devolatilize the melt to slightly reduce the acetaldehyde content, and then add acetaldehyde to reduce agent to further reduce the acetaldehyde content and then shape the improved polymer melt into useful shaped articles. The other pathways represented on Figure 1 show other combinations of operations, all of which lead to the desired result that the shaped article contains the desired low acetaldehyde content, high molecular weight polymer originating from the melt phase without The polymer is subjected to solid state polymerization. The method of the present invention not only avoids the expensive additional steps of the usual solid-state polymerization method, but also the shaped articles produced by this method have both low acetaldehyde content and other excellent properties, such as low molecular weight loss due to degradation, no Defects such as "air bubbles" and "inmelt" are known, but these defects are sometimes formed during molding of a solid-state adjustment material obtained by an ordinary method.

Molding or forming equipment can be any equipment generally known in the art. For example, injection molding can be used to form blanks for blow molding bottles, food/beverage containers, trays, or other desired shaped articles. The polymer melt can be used in extrusion blow molding operations to provide bottles, food containers and the like. Similarly, the polymer melt can be fed into an extruder to make film, sheet, profile, pipe, etc.

The combination of operations illustrated in Figure 1 is not limiting, as it is obvious that other operations can be added and the order of some operations can be changed to achieve the same result.

If polymer pelletizing is desired as an intermediate method, then any moisture absorbed by the polymer must be dealt with. Practitioners of the prior art are aware that the presence of moisture during normal melt processing degrades polyesters. A common method of removing this moisture is to crystallize the polymer to minimize the sticking of the pellets to each other and then subject it to a temperature high enough to remove the vaporized moisture. For a more economical process, the following two methods can be used alone or in combination to provide molten polymer without moisture degradation. Polyester is often extruded into a water bath to cool it so that a slicer can cut it into pellets. Dehydration immediately after slicing can be used to completely remove surface moisture before transferring the polymer to storage. Such dehydration equipment is sold by Gala Industries of Eagle Rock, Virginia, for example. When the storage facility is blanketed or purged with dry gas, the polymer remains dry until just before use. Because the polymer remains dry, no crystallization or drying is necessary. If the polymer is not kept dry, it is amorphous and hydrated and can be fed into an extruder where the melting zone is either purged with gas or a vacuum is used. As the polymer heats up and begins to melt, the high vapor pressure of the water causes water to separate into the vapor space. In order to minimize problems caused by foam, it is preferred to use a machine which first purging the melt zone at ambient pressure, followed by a short residence time in a second zone which is separated by a melt barrier dam created by design Vacuum devolatilization and eventual bulk water removal, the extruder is operated as is commonly done by polymer extruder specialists in the prior art.

During the drying of the melt, in addition to removing water, some other volatile substances are also removed. However, because low acetaldehyde levels are desired for articles intended to come into contact with food, additional devolatilization steps or acetaldehyde-reducing additives are generally required to produce polymer melts of the desired quality.

In some cases, it is desirable to remove some of the acetaldehyde by devolatilization as illustrated in routes K-N. Acetaldehyde can be easily removed from molten polymers in extruder or gear pump equipment by gas purging or subjecting the melt to vacuum. For polyesters with I.V. = 0.4-0.65 produced by any known method, followed by polymer filtration to remove gel and particulate material, followed by another polycondensation reactor to produce high viscosity polyesters with I.V. > 0.68, The typical acetaldehyde content of the polymer obtained from the final reactor before this treatment is generally about 30-300 ppm. The melt can be devolatilized, mixed with additives and used directly, or it can be pelletized for later use. After pelletizing the polymer, it is an amorphous material containing acetaldehyde, which is naturally present in the melt. After remelting with drying, those acetaldehydes will still mostly be removed by using additives and further devolatilization.

Suitable melt processing temperatures for PET polymers are generally from about 260 to about 310°C. In the case of uncured polymers, the melting temperature can be maintained at the lower end of this range. Lower temperatures are known to be beneficial in reducing acetaldehyde content. An advantage of the present invention is that, because the polymeric pellets are amorphous, they can be processed at slightly lower temperatures than those typically used to melt solid conditioned crystalline pellets. Of course, for other types of polyesters, the processing temperature can be adjusted according to melting point, I.V. value, etc.

The method of the present invention is less expensive to operate than the manufacture of crystalline, solid-state adjusted polymers, provides equipment that is energy efficient and reduces capital investment over conventional methods, and produces parisons and molded articles with better clarity, unmelts or other There are far fewer defects or lower concentrations of undesired by-products.

Polymers specifically used in the process include polyethylene terephthalate, polyethylene naphthalate, and poly(ethylene glycol) containing not more than 50 mole percent modified dibasic acids and/or diols. Copolyester. Modified dibasic acids can contain from about 2 to about 40 carbon atoms and include isophthalic, adipic, glutaric, azelaic, sebacic, fumaric, dimer, cis or trans Formula - 1,4-cyclohexanedicarboxylic acid, various isomers of naphthalene dicarboxylic acid, etc. More preferably, the polyesters of the present invention contain at least about 80 mole percent terephthalic acid, naphthalene dioic acid, or mixtures thereof.

The most commonly used naphthalene diacids include the 2,6-, 1,4-, 1,5-, or 2,7-isomers, but 1,2-, 1,3-, 1,6- , 1,7-, 1,8-, 2,3-, 2,4-, 2,5- and/or 2,8 isomers. Dibasic acids can be used in acid form or in their ester form such as dimethyl ester.

Typical modified diols can contain from about 3 to about 10 carbon atoms and include propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, 1,4 - Cyclohexanediol, 1,4-cyclohexanedimethanol and the like. 1,4-Cyclohexanedimethanol can be either cis or trans, or a cis/trans mixture. More preferably, the polyesters of the present invention contain a mixture of at least about 80 mole percent ethylene glycol.

A particularly preferred polyester comprises a mixture of terephthalic acid and about 60 to about 99 mole percent ethylene glycol and about 40 to about 1 mole percent cyclohexanedimethanol.

The polyesters produced in the first step of the invention generally have an I.V. of at least 0.5 dL/g, more preferably at least about 0.65 dL/g, most preferably 0.65-0.85 dL/g.

The polyesters of the present invention are readily prepared using polycondensation reaction conditions known in the art. Typical catalysts which may be used include titanium alkoxides, alone or optionally in combination with acetates or benzoates of zinc, manganese or magnesium and/or catalyst materials well known to those skilled in the art, Dibutyltin dilaurate and antimony oxide or antimony triacetate. Phosphorus compounds and organic toners disclosed in US Patent Nos. 5,384,377 and 5,372,864, incorporated herein by reference, may also optionally be present. Although we refer to the use of continuous polycondensation reactors, batch reactors operating in series can also be used.

Although in this method we refer to the use of polyester in unmodified form, other components such as nucleating agents, branching agents, colorants, pigments, fillers, antioxidants, UV And thermal stabilizers, impact modifiers, etc.

Example

Determination of acetaldehyde content in ethylene terephthalate (PET)

PET samples were dried and extruded as described in the Examples below, and the melt was quenched by collecting in dry ice. Polymers were immediately sliced and stored at -40°C for no more than 2 days prior to acetaldehyde analysis. The stored samples were ground in a Wiley mill to pass through a 20 mesh screen. For analysis, a 0.5 g sample was placed in a test tube and immediately sealed. The samples were analyzed by dynamic surface gas phase analysis using a Hewlett-Packard 5890 Gas Chromatograph with a PerkinElmer Automated Thermal Desorption ATD-50 as the injection system. The acetaldehyde was desorbed by heating the sample at 150°C for 10 minutes. Extruded PET was ground and subjected to the same test to determine standard PET levels.

I.V.

Using standard methods, measure the I.V.

Composition used

The PET used in the sample is a copolyester that includes 100% (mol) terephthalic acid, 98-99% (mol) ethylene glycol and 1-2% (mol) 1,4- Cyclohexanedimethanol has an I.V. of about 0.74. The PET was pelletized and then fed into a vented twin-screw extruder.

Samples simulating high acetaldehyde content were prepared as follows: pelletized PET was placed in a container and the appropriate amount of liquid acetaldehyde was added. The container was sealed and its contents were allowed to equilibrate at room temperature for 1 day before being used in additive experiments.

PET/additive blends were prepared by batch dry blending in bags and then fed to the extruder. The amounts of additives added are as shown in Table 1.

Additive 1 is a high molecular weight (Mw = 38,200) polyester amide prepared from terephthalic acid, cyclohexanedimethanol and hexamethylenediamine, the molar ratio of diol to diamine being 50/50.

Additive 2 is a low molecular weight (Mw = 17,800) polyester amide prepared from terephthalic acid, cyclohexanedimethanol, and hexamethylenediamine in a 50/50 molar ratio of diol to diamine.

Additive 3 is a polyamide prepared from adipic acid and m-xylylenediamine.

Examples 1-12

The polymer/additive composition as shown in Table 1 below was metered into the vented twin screw extruder. The rpm of the extruder screw was maintained at 30 RPM. Extruder Zone 1 was set at 265°C after the water-cooled feed zone. The heated extruder exhaust zones, Zones 2 and 3, were controlled at 272.5°C. The last zone, Zone 4, between the vent and the discharge was maintained at 260°C. To allow the gas to purge the sample, nitrogen preheated to 285°C was used, fed through the extruder vent so that it purges over the polymer melt. The gas flow rate was controlled at 250 sccm by a mass flow controller and vented to atmospheric pressure through a bubble trap. Samples that were not purged had the gas flow turned off, but were still vented to atmospheric pressure through the bubble trap. The residence time of the molten polymer in the extruder after venting was 3 minutes. Examples 1-12 in Table 1 are examples of the invention and demonstrate the excellent ability of various additives to reduce the acetaldehyde content in this extrusion process. For each of these examples, the extruded polymer was formed into rods.

It is clear that a reduction in acetaldehyde content is achieved when the additive is used in combination with a nitrogen purge. The residence time in the extruder (not shown) was sufficient to result in a significant increase in I.V. (0.04-0.09) compared to the control using nitrogen purge. The increase in I.V. value was due to the decrease in the partial pressure of ethylene glycol, This leads to further polycondensation and higher molecular weight polymers.

Table 1

Examples of Additives Influenced on Acetaldehyde Content Example number PrecrsrI.V.(dL/g) Precrsr acetaldehyde content (ppm) additive Nitrogen purge (sccm) Acetaldehyde content of extrudate (ppm) Extrusion IV(dL/g) 1 0.74 2 none 0 4.9 0.61 2 0.74 2 none 250 2.7 0.7 3 0.74 2 A1(1wt%) 0 1.7 0.62 4 0.74 2 A1(1wt%) 250 0.5 0.68 5 0.74 176 none 0 52 0.64 6 0.74 176 none 250 10 0.73 7 0.74 176 A1(1wt%) 0 18 0.63 8 0.74 176 A1(1wt%) 250 1 0.7 9 0.74 176 A2(1wt%) 0 26 0.66 10 0.74 176 A2(1wt%) 250 1.6 0.7 11 0.74 176 A3(0.5wt%) 0 14 0.64 12 0.74 176 A3(0.5wt%) 250 1.4 0.72

Claims (27)

1. A method of manufacturing an article comprising the steps of: a) melt reaction of at least one diol and at least one dicarboxylic acid in the presence of a catalyst substantially free of Co compounds to form a polyester having an I.V. value of at least 0.5 dL/g, wherein the at least one diol is selected from Diols having not more than 10 carbon atoms and mixtures thereof, wherein the dicarboxylic acids are selected from the group consisting of alkyl dicarboxylic acids having 2 to 16 carbon atoms, aryl dicarboxylic acids having 8 to 16 carbon atoms and mixtures thereof, from which molten polyester is obtained; b) adding an acetaldehyde reducing agent to said molten polyester, and subsequently devolatilizing said molten polyester to form a polyester with reduced acetaldehyde content; and c) forming the polyester with reduced acetaldehyde content directly from step b) into an article. 2. Process according to claim 1, wherein said polyester obtained from step a) has an I.V. value of at least 0.65 dL/g. 3. The method of claim 1, wherein said polyester obtained from said step a) has an I.V. value of 0.65-0.85 dL/g. 4. The method of claim 1, wherein said dicarboxylic acid comprises at least 80 mole percent terephthalic acid. 5. The method of claim 1, wherein said dicarboxylic acid comprises at least 80 mole percent naphthalenedioic acid. 6. The method of claim 1, wherein the diol comprises at least 80 mole percent ethylene glycol. 7. The method of claim 1, wherein the diol is a mixture of ethylene glycol and cyclohexanedimethanol. 8. The method according to claim 1, wherein said acetaldehyde reducing agent is selected from the group consisting of polyamides, polyesteramides, nylon 6, aliphatic polyamides, ethylenediaminetetraacetic acid, alkoxylated polyols, di( 4-[beta]-hydroxyethoxyphenyl)sulfone, zeolite compounds, 5-hydroxyisophthalic acid, polyethylene isophthalate, supercritical carbon dioxide, protic acid catalysts, and mixtures thereof. 9. The method of claim 1, wherein the acetaldehyde reducing agent is selected from the group consisting of polyamides, polyesteramides and polyethylene isophthalate. 10. The method according to claim 9, wherein the polyamide is selected from homo- and copolyamides having an AB structure or _{an A2B2} structure. 11. The method of claim 10, wherein the polyamide is selected from the group consisting of polycaprolactam, polyhexamethylene adipamide, polym-xylylene adipamide, and mixtures thereof. 12. The method of claim 10, wherein the polyesteramide is selected from the group consisting of polyethyleneimine, polyesteramide prepared from terephthalic acid, 1,4 cyclohexanedimethanol, isophthalic acid and hexamethylenediamine, Polyesteramide prepared from terephthalic acid, 1,4-cyclohexanedimethanol, adipic acid and hexamethylenediamine, from terephthalic acid, 1,4-cyclohexanedimethanol and bis(p-aminocyclohexyl ) Polyesteramides prepared from methane and mixtures thereof. 13. The method according to claim 1, wherein said acetaldehyde reducing agent is added in an amount of 0.1-5% by weight. 14. The method according to claim 1, wherein said acetaldehyde reducing agent is added in an amount of 0.2-3% by weight. 15. The method of claim 1, wherein said dicarboxylic acid comprises terephthalic acid, and said diol is 60-99% (mol) ethylene glycol and 40-1% (mol) cyclohexanediol Methanol mixture. 16. The method of claim 1, wherein the reacting and devolatilizing steps are performed in a single piece of equipment. 17. The method of claim 1, wherein said acetaldehyde reducing agent is added separately to said polyester. 18. The method of claim 1, wherein the acetaldehyde reducing agent is added to the polyester as part of a concentrate. 19. The method of claim 1, wherein at least one organic toner is added in said melting reaction step a). 20. The method of claim 1, wherein said devolatilization is performed at a pressure greater than 25 mmHg. 21. The method of claim 1, wherein said devolatilization is performed at or near atmospheric pressure. 22. The method of claim 1, wherein said devolatilization is performed with a residence time short enough to ensure that the I.V. value does not increase significantly. 23. The method of claim 22, wherein said significant increase is greater than 0.1 dL/g. 24. The method of claim 22, wherein said significant increase is greater than 0.05 dL/g. 25. The method of claim 22, wherein said significant increase is greater than 0.03 dL/g. 26. The method of claim 1, wherein said polyester has an acetaldehyde content of less than 10 ppm. 27. An article made according to the method of claim 1 selected from the group consisting of molded, formed and extruded articles.